In general, when a metal material has a small size, such as a nanometer unit, the metal material has physical and chemical properties that are completely different from when they are in the existing bulk state. For example, when gold, which is one of the metal material, becomes a gold (Au) nanoparticle in a nanometer size, gold (Au) nanoparticle has unique properties different from that when it is in the bulk state, which is significantly useful for photoelectrons, electronic devices, bio-devices, sensors, and the like, depending on the unique properties.
Specifically, when light is irradiated on a surface of the gold (Au) nanoparticles, resonance between the light and a free electron of the gold is generated and shows unique optical properties such as scattering, absorption, and the like. Therefore, even though a shape and a size of the metal nanoparticles are slightly changed, a noticeable difference occurs in view of spectroscopy patterns.
In recent years, a novel structure is formed by using precise linker molecules such as a number of thiol groups having various lengths or various kinds of functional groups or DNA to assemble the gold (Au) nanoparticles, which is significantly used as a nano photonic device or optical materials.
In addition thereto, synthesis of the gold (Au) nanoparticles has actively been conducted as a basis for research searching properties of the nanoparticles, and various shaped gold (Au) nanoparticles such as octahedron, cube, decahedron, rod, and the like, have been synthesized by various methods until now.
However, even though the research related to synthesis of the gold (Au) nanoparticles has been conducted, synthesis of pure gold spherical nanoparticles having a size of 100 nm or more has not been reported yet.
Meanwhile, technology of synthesizing isotropic shaped nanoparticles having a size of 100 nm or less by a controlling process using surfactant in a bottom-up scheme has already been known in the art. However, when the nanoparticles to be manufactured are synthesized to have a size of 100 nm or more, it is not within the growing controllable range of the surfactant, such that a difference in a growing rate eventually occurs between crystal planes, such that a problem occurs in the nanoparticles only having non-isotropic shape are obtained.
Nevertheless, spherical shapes capable of simplifying assembly of the particles and performing a symmetrical assembly are industrially utilized, and in particular, the spherical gold (Au) nanoparticles has gradually received attention due to high optical utilization.
Therefore, there is a need for the development of a manufacturing method which is appropriate for producing a thermally stable and uniformly spherical gold nanoparticle having a size of 100 nm or more.